DESCRIPTION (Investigators' abstract): Heparin employed in the nearly 15 million extracorporeal procedures performed annually often leads to a high incidence (8-33%) of bleeding complications. Protamine employed in heparin reversal, however, can cause serious and at times fatal cardiovascular responses. Indeed, the combined use of heparin and protamine has been considered a major cause of morbidity and mortality for patients undergoing cardiovascular surgery. We previously proposed an approach which would simultaneously prevent both heparin and protamine induced complications. The approach consists of placing a blood filter device containing immobilized protamine (termed "protamine filter") at the distal end of an extracorporeal device. The project received a FIRST Award in 1987, followed by a highly merited 5 year competing renewal (Percentile: 6.9%) in 1993 to further continue our pursuit in this area. During this past grant period (1993-96), remarkable progress has been achieved; as reflected by the publication of 31 manuscripts and 5 patents. A highly effective protamine filter and a sensor-directed bio-feedback heparin-removing system are both established. In addition, a first ever sensor for blood heparin monitoring has been developed and is presently on the market for research uses. After the conclusion of our on-going animal studies (by 1997), every aim proposed in the previous application will be completely achieved. Since all the fundamental research related to this project has been addressed during the two grant periods, we plan in this competing renewal application to shift our long-time research on extracorporeal heparin removal toward a new direction. This new research direction is to develop an intravenous heparin-neutralizing agent which provides all the advantages of protamine and yet lacks its toxic effects. As gathered from the consensus of clinicians routinely engaged in heparin and protamine therapy, this would be the ultimate solution to achieve safe clinical heparin reversal. An explicit review of the mechanisms of heparin neutralization and protamine toxicity suggests that a chain-shortened low molecular weight protamine (LMWP) species, if it can be derived from protamine to contain the intact, arginine-rich heparin-binding domain but not the futile and yet etiologic region in protamine, could simply be this ideal anti-heparin agent. In addition, the LMWP would also be devoid of immunogenicity and antigenicity; both are known to contribute mightily to protamine toxicity. Preliminary studies have yielded promising results to verify our hypotheses. In this application, we plan to build upon these initial findings and follow the precedent methodology in deriving low molecular weight heparins (LMWH) to further develop the LMWP species. These compounds will then be tested in vitro and in vivo of the efficacy and toxicity against both heparin and LMWH.